The reason I mention the ability to set variables is because it's the only way I know of to set variables when working in an Xcode Playground.

I recently wanted to see a backtrace for a strange CGContext error I was getting when working with a "live" view in a playground. By default, the backtrace isn't shown in the console, so I had to set the CG_CONTEXT_SHOW_BACKTRACE environment variable to see what was up:

setenv("CG_CONTEXT_SHOW_BACKTRACE", "1", 1)

After that, it was smooth sailing. Well, other than the CGContext error I was getting, but that's a topic for another day.

Hope this helps!

P.S. The above functions require the Darwin module to be imported. Foundation automatically imports Darwin, but I thought I should mention it nonetheless.